1. Field of the Invention
This invention generally relates to a fluorescent display device, and more particularly to a fluorescent display device in which dot-shaped anodes are arranged in the form of a matrix so as to display numerals, characters, graphic forms and the like.
2. Description of the Prior Art
A fluorescent display device, in which thermions emitted from a heated filamentary cathode are made to impinge on phosphor-coated anodes so as to effect displays, is widely used as the display device of electronic equipment or the like, because of its fine color of light emitted, capability of being driven on a low voltage, low power consumption, etc. In the fluorescent display device which is generally known as a dot-matrix type, the phosphor-coated anodes are arranged in the form of a matrix and connected together on a row-by-row basis, while disposing control electodes above the anodes on a column-by-column basis in opposed relationship thereto, and the anode positioned at the point of the intersection of the selected row and column is made to luminesce. The recent diversification of informations produced by various electronic equipment requires a fluorescent display device having the display dots arranged in a high density so as to effect the display with a high resolving power.
In order to arrange the display dots in the high density, two technical problems must be settled. The first problem is a display defect created at an edge of anodes A as shown in FIG. 8 which is resulted from a deflection of passages of electrons e from a cathode C to the anodes A by a negative electric field created by control electrodes G' adjacent to a control electrode G opposite to the anode A to be energized. This display defect is created, because intervals between each of the control electrodes become narrow in association with the arrangement of the anodes in the high density. In the fluorescent display device of this type, a dynamic driving system is generally used so as to decrease a number of outer terminals connected to each of the anodes and to scan the control electrodes which are provided in number corresponding to the increased number of the anodes. Accordingly, the ratio of selecting period of one control electrode to one cycle of the scanning which is known as duty factor becomes smaller, which results in making the pulse width for scanning one control electrode narrow and decreasing luminance at the anodes. This is the second problem. In order to compensate the decreased luminance, the driving voltage must be increased contrary to the advantages of the fluorescent display device being driven at the low voltage.